Three separate investigations are being carried out. One of these is concerned with studies relating to fatty acids, another to cholesterol, and the last to carotenes. Our studies on the biosynthesis of fatty acids are concerned with the structural organization and the mechanism of action of pigeon and rat liver fatty acid synthetases. They are also concerned with the identification of the factors that control the rates of synthesis and degradation of rat liver fatty acid synthetase and with the mechanisms by which these controls are effected. Studies on the biosynthesis of cholesterol are concerned primarily with the purification of enzymes that effect the conversion of Beta-hydroxy-Beta-methylglutaryl-CoA to squalene and with the mechanisms of these reactions. These studies are also concerned with the identification of the factors that control the rate of synthesis of the rate-limiting enzyme of cholesterol synthesis in rat liver. Studies on the biosynthesis of carotenes are concerned with the complete identification of the pathway of conversion of isopentenyl pyrophosphate to cyclic carotenes and with the isolation, purification and mechanisms of action of the enzymes that effect the synthesis of these compounds.